The present invention relates to a printing device, and more particularly, to a printing device provided with two sheet feed trays on a top surface of a body case, which trays are capable of feeding sheet into a printing mechanism.
Conventionally, printing devices are provided with a fixed sheet feed tray or a removable sheet feed tray, usually called a sheet feed cartridge, for feeding each one of sheets to be printed into a printing region. Since printing devices are required to have a more compact structure than photocopying devices and since a sheet conveying mechanism and a printing mechanism inside the printing device must operate in interlocking relation with each other during the printing operation, conventional printing devices have been equipped with only one fixed or removable sheet feed tray for feeding sheet. Thus, conventional printing devices can provide only one type of sheet during a printing process. Moreover, when using removable sheet feed trays with conventional printing devices, only one tray of a plurality of feed trays, each containing a different size of printing sheet, is selectively mounted in the printing device.
Since only one sheet feed tray is mounted in conventional printing devices, such inconvenient operations as exchanging sheet or removable sheet feed trays are frequently necessary when printing on different sizes of sheet. Further, the sheet supply in the trays must be frequently replenished because the number of sheets that can be contained in the trays is limited.
Further, conventional removable sheet feed trays are mounted horizontally in a mounting section on the front or back surface of a body case so that about one-half the length of the sheet feed tray is extending out of the body case. Therefore, the overall front-to-back length of the printing device is large, and the printing device occupies much space.
In another aspect, conventional fixed sheet feed trays include a sheet receiving unit for receiving and guiding numerous sheets of sheet, and a slider for regulating the sheet width. On the other hand, conventional removable sheet feed trays include a box-shaped cassette case, a sheet receiving plate provided on the bottom portion of the cassette case for receiving sheet, and a cover plate detachably mounted on the top surface of the cassette case. Sheet feed rollers are not mounted in the removable sheet feed trays. Instead, sheet conveying mechanism including a set of sheet feed rollers is fixedly mounted in the body case of the conventional printing devices.
Since the sheet conveying mechanism including the set of sheet feed rollers is fixedly mounted in the body case, it is difficult to mount a plurality of sheet feed trays in the body case. In other words, since the sheet feed trays must be positioned near the set of sheet feed rollers in order for the rollers to feed sheet from the trays, it is not remotely possible to configure the printing device so that one set of sheet feed rollers can supply sheet from a plurality of sheet feed trays. In addition, the configuration of the printing device must be such that sheet becoming jammed in the sheet feed passage can be removed. However, this is difficult when supplying sheet from a plurality of trays because of restrictions on the structure of the sheet feed passage.
Japanese Patent Application Kokai (OPI) No. HEI-2-53340 discloses a copying machine in which a plurality of removable sheet feed trays are mounted in a body case, and feed rollers corresponding to these sheet feed trays are provided inside the body case, enabling sheet to be alternatively fed from any of the plurality of sheet feed trays. However, the mounting sections for the plurality of sheet feed trays are provided at a plurality of levels, increasing the overall height of the body case.
If this arrangement is applied into a printer, a body case of the printer becomes bulky so as to install a plurality of sheet feed trays arrayed in a vertical direction. Intricate sheet feed mechanism and its driving system result.
In still another aspect, the sheet feed mechanism of the printer is provided for feeding the sheet fed from the sheet feed tray to the printing mechanism. The sheet feed mechanism includes a register roller and a sheet detection mechanism positioned upstream of the register roller for detecting a leading edge of the sheet. The sheet detection mechanism detects the leading edge of the sheet, and the leading end of the detected sheet is brought into abutment with the register roller so as to control sheet feeding amount after the abutment. The sheet detection mechanism includes a detection piece pivotally movable toward and away from the sheet feed passage, one or a plurality of lever members positioned at one widthwise side of the sheet feed passage and movable in interlocking relation with the detection piece, and a sensor for detecting the movement of the lever members. Therefore, if a plurality of sheet feed trays are installed on the body case, a plurality of detecting pieces must be provided and therefore, a plurality of sensors must be correspondingly required. This may be costly due to the increase in electrical components and complexity in a control arrangement.
Further, if a plurality of sheet feed trays are installed on the body case of the printing device, complex sheet feed passages result, since the plurality of sheet feed passages from the plurality of sheet feed trays reach the common register roller. Furthermore, one sheet feed passage may become excessively long or may be hidden behind other mechanism. As a result, it becomes difficult to provide a wide open space over the sheet feed passage so as to deal with sheet jamming.
Moreover, it becomes difficult to position the sheet detection piece of the sheet detection mechanism in the vicinity of the register roller in such a complicated sheet feed passages. Further, the sheet detection piece must be located at a place capable of facilitating inspection and maintenance thereof. However, the sheet detecting mechanism requires large installation space. Accordingly, it would be extremely difficult to dispose a plurality of sheet detection mechanisms in the body case. If the detection piece is positioned remote from the register roller, sheet feeding accuracy may be lowered.